A US senator has said an estimated 4,700 people, including some civilians, have been killed in bombing raids conducted under America’s secretive drone war, local media reported Wednesday.

The toll from hundreds of drone-launched missile strikes against suspected Al-Qaeda militants in Pakistan, Yemen and elsewhere has remained a mystery, as US officials refuse to publicly discuss any details of the covert campaign.

But Republican Senator Lindsey Graham, a staunch supporter of drone use, openly cited a number that exceeds some independent estimates of the toll.

“We’ve killed 4,700,” Graham was quoted as saying by the Easley Patch, a local website covering the small town of Easley in South Carolina.

“Sometimes you hit innocent people, and I hate that, but we’re at war, and we’ve taken out some very senior members of Al-Qaeda,” Graham reportedly told the Easley Rotary Club.

Despite criticism from some lawmakers and rights advocates who have questioned the secrecy and the legality of the drone attacks, Graham defended President Barack Obama’s reliance on the unmanned, robotic aircraft.

“It’s a weapon that needs to be used,” Graham said. “It’s a tactical weapon. A drone is an unmanned aerial vehicle that is now armed.”

It was not clear if Graham was referring to the US government’s own estimate of casualties from drone strikes. His office was not immediately available for comment.

Using press reports and other sources, several organizations have tried to calculate how many militants and civilians may have been killed in the drone strikes, which have been expanded dramatically under Obama’s administration.

The Washington-based New America Foundation says there have been 350 US drone strikes since 2004, most of them during Obama’s presidency. And the foundation estimates the death toll at between 1,963 and 3,293, with 261 to 305 civilians killed.

According to the London-based Bureau of Investigative Journalism, between 2,627 and 3,457 people have been reportedly killed by US drones in Pakistan since 2004, including between 475 and nearly 900 civilians.

The casualty estimates are related to covert strikes run by the CIA, and not drone bombing raids in Afghanistan which are under the US military’s authority and not cloaked in secrecy.

The Obama administration has insisted the “targeted killings” are “a last resort” against those plotting to attack the United States but who cannot be captured.

Opponents, however, say the drone strikes amount to extrajudicial assassinations that sow resentment among local populations and lack oversight by Congress or courts.

Obama acknowledged for the first time this month that Americans needed more than just his word to be assured he was not misusing his powers in waging a secret drone war overseas.